Tear film proteins attached to soft contact lenses

Purpose Contact lenses (CLs) float on the tear film that is the outer 7-8 µm liquid layer on the cornea. Proteins can adhere to the surface of CLs. Adhered proteins are the agent for irritation and in case of long wear time and poor hygiene, possibly also for keratitis; as the proteins may serve as an anchor for bacteria to attach to. We have isolated and identified such adhered proteins from the CL surface. Methods Soft CLs from 3 non-atopic human individuals were collected. 1-day, 14-days and 30-days lenses were examined. Adhered proteins were removed in denaturing lysis buffer and separated on two-dimensional polyacrylamide gels that were silver stained. Spots of interest were excised and subjected to in-gel tryptic digestion prior to liquid chromatography - tandem mass spectrometry analysis. Results Equal amounts of proteins (20-40 µg) were separated on 2D-gels. Protein patterns appeared more intense but with similar patterns with longer wear-period. A fraction of the observed silver stained protein spots were successfully identified with tandem mass spectrometry. Identified proteins included: lactoferrin, lysozyme C, lipocalin-1, mammaglobulin, beta-2-microglobulin, prolactin-inducible protein, immunoglobulins, polymeric immunoglobulin receptor, zinc-alpha-2-glycoprotein, cystatin-S, cystatin-SN, secretoglobulin family 1D member 1 and serum albumin. Conclusion Adhered proteins from CLs were isolated and identified. The protein composition resembles the protein composition in tears. The combined techniques of 2D-gel electrophoresis and mass spectrometry is proven to be a suitable tool to examine proteins adhered to CLs. Proteins from a single set of CLs can be analyzed.